Thin interface layer to improve copper etch stop

ABSTRACT

In accordance with the objectives of the invention a new method is provided for improving adhesion strength that is deposited over the surface of a layer of copper. Conventional etch stop layers of for instance dichlorosilane (SiCl 2 H 2 ) or SiOC have poor adhesion with an underlying layer of copper due to poor molecular binding between the interfacing layers. The surface of the deposited layer of copper can be provided with a special enhanced interface layer by using a method provided by the invention. That is pre-heat of the copper layer followed by a pre-cleaning treatment with ammonia (NH 3 ) and N 2 , followed by forming an adhesive enhanced layer over the copper layer by treatment with N 2  or O 2  or N 2  with alkyl-silane or alkyl silane.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] The invention relates to the fabrication of integrated circuitdevices, and more particularly, to a method to improve the etch stopwhen etching copper surfaces.

[0003] (2) Description of the Prior Art

[0004] The creation of semiconductor devices requires the deposition andpatterning of numerous layers of semiconductor material, which are thenpatterned and etched to form device features of required dimensions andelectrical performance characteristics. After the semiconductor devicesessentially have been created, device elements may have to beinterconnected in order to create functional entities. As interconnectmaterials are typically used metallic materials comprising for instancealuminum, tungsten, titanium, copper, polysilicon, polycide or alloys ofthese metals. Interconnects are formed by first depositing a layer ofmetallic material and then patterning and etching the layer of metallicmaterial to form the desired interconnect pattern. Layers of wiringmaterial are typically about 1,000 to 10,000 Angstrom thick, morepreferably about 4,000 Angstrom. Wiring that serves as interconnectlines is typically about 1,000 and 8,000 Angstrom wide, more preferablyabout 5,000 Angstrom wide. In addition to forming interconnect traces,contact plugs or vias also form an integral part of an interconnectnetwork. Plugs can be formed using a conducting or metallic substancesuch as copper, tungsten, wolfram, titanium nitride, molybdenum,silicide and polysilicon, tantalum or a silicide (including, forexample, TiSix, WSix, NiSix, MoSix, TaSix, PdSix, CoSix and others).

[0005] As part of the creation of metal interconnects, layers that servepurposes other than forming a conductive interface between points arefrequently applied for reasons of device performance requirements andreliability. Such layers include for instance the well known applicationof a layer of seed material, to enhance adhesion between overlyinglayers of which the upper layer is a conductive layer, or barrierlayers, to prevent diffusion of metallic substance into surroundingdielectrics.

[0006] A number of methods are widely used for the creation of a layerof conductive material such as methods of sputter, electro orelectroless metal deposition and methods of CVD. For instance, EDS bathprocessing can be applied for the creation of a layer of copper at atemperature between about 25 and 50 degrees, the source of depositionbeing the dilution of H₂SO₄, CuSO₄ and HCl with a deposition flow rateof between about 15K and 20 K sccm, a deposition time of between about 1and 10 minutes, a voltage being applied to the anode of the EDS bath ofbetween about 0.1 and 2 volts and a voltage being applied to the cathodeof between about 0.1 and 2 volts. The EDS process is particularly suitedfor the creation of copper metal plugs, since the copper plug is createdin a well-controlled manner due to the fact that EDS Cu deposits copperonly on places that have a copper seed layer.

[0007] Interconnect contacts or vias are typically created by firstdepositing a layer of dielectric over a metallic layer, preferablecomprising copper, etching openings through the layer of dielectric inthe locations where the interconnect contacts or vias are to be locatedand filling the created openings with a conductive substance,electrically contacting the underlying layer of copper. The etch of thelayer of dielectric requires a layer of etch stop material whicheffectively stops the etch through the layer of dielectric at thesurface of the underlying layer of copper. The layer of etch stopmaterial must have good adhesion to the underlying copper surface inorder to prevent problems of etch or adhesion of the overlying layer ofdielectric resulting in problems of device reliability. The inventionprovides such a layer by providing an adhesion promotion layer for theadhesion of an etch stop layer that has been deposited over a coppersurface. The layer of adhesion promotion material of the inventionassures strong adhesion to the underlying copper surface and to theoverlying etch stop layer.

[0008] U.S. Pat. No. 6,136,680 (Lai et al.) shows a SiC layer on copper30, see FIG. 6.

[0009] U.S. Pat. No. 6,100,587 (Merchant et al.) shows SiC barrierlayers in a copper interconnect process.

[0010] U.S. Pat. No. 5,946,601 (Wong et al.) reveals a carbon-containingbarrier layer.

SUMMARY OF THE INVENTION

[0011] A principle objective of the invention is to provide a layer overthe surface of copper that serves as an adhesion promotion layer betweencopper and an etch stop layer.

[0012] Another objective of the invention is to eliminate concerns ofpeeling or delamination between the surface of a layer of copper and anoverlying etch stop layer.

[0013] In accordance with the objectives of the invention a new methodis provided for improving adhesion strength that is deposited over thesurface of a layer of copper. Conventional etch stop layers of forinstance dichlorosilane (SiCl₂H₂) or SiOC have poor adhesion with anunderlying layer of copper due to poor molecular binding between theinterfacing layers. The surface of the deposited layer of copper can beprovided with a special enhanced interface layer by using a methodprovided by the invention. That is pre-heat of the copper layer followedby a pre-cleaning treatment with ammonia (NH₃) and N₂, followed byforming an adhesive enhanced layer over the copper layer by treatmentwith N₂ or O₂ or N₂ with alkyl-silane or alkyl silane.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 shows a cross section of a prior art method of formingcopper plugs overlying a layer of copper

[0015]FIG. 2 shows a cross section of the invention of forming copperplugs overlying a layer of copper.

[0016]FIG. 3 provides an explanation of the molecular interactionprovided by the invention between a copper surface and an overlying etchstop layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Referring now specifically to a prior art method of formingcopper plugs overlying a layer of copper, which is shown in crosssection in FIG. 1. The cross section of FIG. 1 shows:

[0018]10, a semiconductor surface, typically the surface of asemiconductor silicon substrate

[0019]12, a first layer of dielectric deposited over the surface oflayer 10

[0020]14, a second layer of dielectric deposited over the surface of thefirst Etch Stop Layer (ESL) 12 of dielectric

[0021]16, first copper plugs formed in the first layer 12 of dielectric

[0022]18, second copper plugs formed in the second layer 14 ofdielectric; copper plugs 18 align with copper plugs 16

[0023]20, a first Etch Stop Layer (ESL) created over the surface of thefirst layer 12 of dielectric, and

[0024]22, a second Etch Stop Layer (ESL) created over the surface of thesecond layer 14 of dielectric.

[0025] The methods and procedures that are used to create theinterconnect arrangement that is shown in cross section in FIG. 1 arewell known in the art. This and the observation that these methods arenot germane to the invention obviate a need for further explanation ofthese methods and procedures at this time.

[0026] Referring now specifically to the cross section that is shown inFIG. 2, there is shown:

[0027]10, a semiconductor surface, typically the surface of asemiconductor silicon substrate

[0028]12, a first layer of dielectric deposited over the surface oflayer 10

[0029]14, a second layer of dielectric deposited over the surface of thefirst Etch Stop Layer (ESL) 24

[0030]16, first copper plugs formed in the first layer 12 of dielectric

[0031]20, a first Etch Stop Layer (ESL) created over the surface of thefirst adhesion promotion layer 24

[0032]18, second copper plugs formed in the second layer 14 ofdielectric; copper plugs 18 align with copper plugs 16, and, optionally

[0033]22, a second Etch Stop Layer (ESL) created over the surface of thesecond adhesion promotion layer 26

[0034]24, a first adhesion promotion layer created over the surface ofthe first layer 12 of dielectric

[0035]26, a second adhesion promotion layer created over the surface ofthe second layer 14 of dielectric.

[0036] In comparing the prior art method as reflected by the crosssection of FIG. 1 with the invention as reflected by the cross sectionof FIG. 2, it is clear that the invention has added layers 24 and 26,that is an adhesion promotion interface between an overlying etch stoplayer and underlying copper. Layer 24 and, optionally layer 26, can becreated following one of four methods, as follows:

[0037] 1. pre-heat the surface of the layer of copper, that is thesurface of layer 16 (and optionally the surface of layer 18), followedby a Plasma Enhanced CVD treatment of surface of the layer of copperusing ammonia (NH₃) as a source gas

[0038] 2. pre-heat the surface of the layer of copper, that is thesurface of layer 16 (and optionally the surface of layer 18), followedby a Plasma Enhanced CVD treatment of surface of the layer of copperusing ammonia (NH₃)+N₂ as source gasses

[0039] 3. pre-heat the surface of the layer of copper, that is thesurface of layer 16 (and optionally the surface of layer 18), followedby a Plasma Enhanced qVD treatment of surface of the layer of copperusing ammonia (NH₃)+alkyl-silane as source gasses, and

[0040] 4. pre-heat the surface of the layer of copper, that is thesurface of layer 16 (and optionally the surface of layer 18), followedby a Plasma Enhanced CVD treatment of surface of the layer of copperusing (NH₃)+N₂ +alkyl-silane as source gasses.

[0041] Alkyl-silane is known to have a chemical composition ofCH_(x)R_(4−x) where x=1, 2 or 3 and R is methyl (CH₃) or ethyl (C₂H₅) orpropyl (C₃H₇) etc., in accordance with the composition C_(n)H_(2n+1).

[0042] Typical PECVD processes can be performed for the treatment of thesurface of the layer of copper in a low pressure environment at achamber pressure between about 0.3 Torr and 1.0 Torr, a temperaturebetween about 300 and 450 degrees C. with a selection of the aboveindicated reactant gases at a flow rate between about 10 and 10,000 sccmin a diluent carrier gas PH₃ at a flow rate of between about 20 and 300sccm, for a time of between about 3 seconds and 30 minutes.

[0043] The above indicated pre-heat the surface of the underlying layerof dielectric can be performed by applying a temperature between about200 and 600 degrees C. at atmospheric pressure for a time between about2 and 5 minutes.

[0044] The above indicated processing sequences uses as initial surfaceof the layer of copper a polished layer of copper, polished usingmethods of CMP. Pre-heating the surfaces of the layer of copper and thelayer of dielectric removes any H₂O from those surfaces in preparationof the PECVD treatment of the surface. The ammonia (NH₃) that is used asa source gas during the. PECVD process moves copper oxide (CuO) from thesurface of the layer 16 (optionally layer 18) of copper.

[0045] The grazing angle FTIR spectrum is a specially designed FTIR witha very high sensitivity. The spectrum shows, with significantly improvedsensititity, the same information as is typically shown with aconventional FTIR, that is molecular vibration wavenumber, e.g. Cu—Nvibration peak at 482 cm⁻¹ or Cu—O stretch at 652 cm⁻¹.

[0046]FIG. 3 further explains the molecular action that is created bythe invention, as follows;

[0047]24 shows a cross section of a layer of copper on the surface ofwhich the adhesion promotion layer of the invention is created, similarto layer 16 of FIG. 2

[0048]26 is the adhesion promotion layer of the invention, similar tolayer 24 of FIG. 2; molecular interaction taking place over the surfaceof layer 24 is stimulated by the nitrogen (N) and hydrogen (H) richenvironment that is created by the PECVD treatment of the invention;this PECVD treatment leads to creating copper-to-nitrogen (Cu—N) bondsas for example bonds 23 and 25. These Cu—N bonds improve the interfacebetween the layer 24 of copper and the overlying layer 26 of adhesionpromotion layer

[0049]28, a Etch Stop Layer (ESL) overlying the adhesion promotionlayer, similar to layer 20 of FIG. 2

[0050]27 and 29, the silicon that is provided by the alki-silane of thePECVD process of the invention further creates bonds 27 and 29,enhancing adhesion between layer 26 of adhesion promotion layer and theoverlying layer 28 of ESL. For many applications of a layer of ESL amaterial can be selected that comprises a silicon component, forinstance dielectrics such as silicon dioxide (“oxide”, doped or undoped)or silicon nitride (“nitride”), silicon oxynitride, silicon carbide(SiC), silicon oxycarbide (SiOC) and silicon nitro carbide (SiNC).

[0051] The indicated creation of molecular bonds such as bonds 23, 25,27 and 29 assures that the surface treatment of the invention leads tomeeting the objectives of the invention that is:

[0052] 1. to provide a layer over the surface of a layer of copper thatserves as an adhesion promotion layer and that has good adhesion to thesurface of the layer of copper, and

[0053] 2. to eliminate concerns of peeling or delamination between thesurface of a layer of copper and an overlying layer of ESL.

[0054] Although the invention has been described and illustrated withreference to specific illustrative embodiments thereof, it is notintended that the invention be limited to those illustrativeembodiments. Those skilled in the art will recognize that variations andmodifications can be made without departing from the spirit of theinvention. It is therefore intended to include within the invention allsuch variations and modifications which fall within the scope of theappended claims and equivalents thereof.

What is claimed is:
 1. A method to create a thin interface layer overthe surface of a layer of copper that serves as an adhesion promotionlayer and improves adhesion between a layer of copper and an overlyingEtch Stop Layer (ESL), comprising the steps of: providing a substrate,said substrate having been provided with at least one layer of copperover the surface thereof; pre-heating the surface of said at least onelayer of copper; pre-cleaning the surface of said at least one layer ofcopper; forming an adhesive enhanced layer over the surface of said atleast one layer of copper; and depositing an etch stop layer over thesurface of said adhesive enhanced layer.
 2. The method of claim 1, saidpre-heating comprising applying a temperature between about 200 and 600degrees C. at atmospheric pressure for a time between about 2 and 5minutes.
 3. The method of claim 1, said pre-cleaning the surface of saidat least one layer of copper is submitting the surface of said at leastone layer of copper to a Plasma Enhance CVD treatment using NH₃ and N₂as source gasses.
 4. The method of claim 1, said forming an adhesiveenhanced layer over the surface of said at least one layer of copper isexposing the surface of said at least one layer of copper to a PlasmaEnhanced CVD (PECVD) treatment in a low pressure environment at achamber pressure between about 0.3 Torr and 1.0 Torr, a temperaturebetween about 300 and 450 degrees C. exposing the surface of said atleast one layer of cooper to a source gas.
 5. The method of claim 4,said source gas being selected from the group consisting of N₂ and O₂and N₂ with alkylsilane and alkylsilane.
 6. The method of claim 4, saidsource gasses being applied at a flow rate between about 10 and 10,000sccm, for a time of between about 3 seconds and 30 minutes.
 7. A methodto create a thin interface layer over the surface of a layer of copperthat serves as an adhesion promotion layer and improves adhesion betweena layer of copper and an overlying layer of ESL, comprising the stepsof: providing a substrate, said substrate having been provided with atleast one layer of copper over the surface thereof; pre-heating thesurface of said at least one layer of copper by applying a temperaturebetween about 200 and 600 degrees C. at atmospheric pressure for a timebetween about 2 and 5 minutes; pre-cleaning the surface of said at leastone layer of copper by submitting the surface of said at least one layerof copper to a Plasma Enhance CVD treatment using NH₃ and N₂ as firstsource gasses; forming an adhesive enhanced layer over the surface ofsaid at least one layer of copper by exposing the surface of said atleast one layer of copper to a Plasma Enhanced CVD (PECVD) treatment ina low pressure environment at a chamber pressure between about 0.3 Torrand 1.0 Torr, a temperature between about 300 and 450 degrees C.exposing the surface of said at least one layer of cooper to a secondsource gas; and depositing an etch stop layer over the surface of saidadhesive enhanced layer.
 8. The method of claim 7, said second sourcegas being selected from the group consisting of N₂ and O₂ and N₂ withalkylsilane and alkylsilane.
 9. The method of claim 7, said secondsource gasses being applied at a flow rate between about 10 and 10,000sccm, for a time of between about 3 seconds and 30 minutes.
 10. A methodto create a thin interface layer over the surface of a layer of copperthat serves as an adhesion promotion layer and improves adhesion betweena layer of copper and in overlying layer of ESL, comprising the stepsof: providing a substrate, said substrate having been provided with atleast one layer of copper over the surface thereof; pre-heating thesurface of said at least one layer of copper by applying a temperaturebetween about 200 and 600 degrees C. at atmospheric pressure for a timebetween about 2 and 5 minutes; pre-cleaning the surface of said at leastone layer of copper by submitting the surface of said at least one layerof copper to a Plasma Enhance CVD treatment using NH₃ and N₂ as firstsource gasses; forming an adhesive enhanced layer over the surface ofsaid at least one layer of copper by exposing the surface of said atleast one layer of copper to a Plasma Enhanced CVD (PECVD) treatment ina low pressure environment at a chamber pressure between about 0.3 Torrand 1.0 Torr, a temperature between about 300 and 450 degrees C.exposing the surface of said at least one layer of cooper to a secondsource gas, said second source gas being selected from the groupconsisting of N₂ and O₂ and N₂ with alkylsilane and alkylsilane; anddepositing an etch stop layer over the surface of said adhesive enhancedlayer.
 11. The method of claim 10, said second source gas being appliedat a flow rate between about 10 and 10,000 sccm, for a time of betweenabout 3 seconds and 30 minutes.
 12. A method to create a thin interfacelayer over the surface of a layer of copper that serves as an adhesionpromotion layer and improves adhesion between a layer of copper and anoverlying layer of ESL, comprising the steps of: providing a substrate,said substrate having been provided with at least one layer of copperover the surface thereof; pre-heating the surface of said at least onelayer of copper by applying a temperature between about 200 and 600degrees C. at atmospheric pressure for a time between about 2 and 5minutes; pre-cleaning the surface of said at least one layer of copperby submitting the surface of said at least one layer of copper to aPlasma Enhance CVD treatment using NH₃ and N₂ as first source gasses;forming an adhesive enhanced layer over the surface of said at least onelayer of copper by exposing the surface of said at least one layer ofcopper to a Plasma Enhanced CVD (PECVD) treatment in a low pressureenvironment at a chamber pressure between about 0.3 Torr and 1.0 Torr, atemperature between about 300 and 450 degrees C. exposing the surface ofsaid at least one layer of cooper to a second source gas, said secondsource gas being selected from the group consisting of N₂ and O₂ and N₂with alkylsilane and alkylsilane, said source gasses being applied at aflow rate between about 10 and 10,000 sccm, for a time of between about3 seconds and 30 minutes; and depositing an etch stop layer over thesurface of said adhesive enhanced layer.
 13. A method to create a thininterface layer over the surface of a layer of copper that serves as anadhesion promotion layer and improves adhesion between a layer of copperand an overlying layer of ESL, comprising the steps of: providing asubstrate, said substrate having been provided with at least one layerof copper over the surface thereof; pre-heating the surface of said atleast one layer of copper; pre-cleaning the surface of said at least onelayer of copper by applying a first process of PECVD to the surface ofsaid at least one layer of copper; forming an adhesive enhanced layerover the surface of said at least one layer of copper by applying asecond process of PECVD to the surface of said at least one layer ofcopper; and depositing an etch stop layer over the surface of saidadhesive enhanced layer.
 14. The method of claim 13, said pre-heatingcomprising applying a temperature between about 200 and 600 degrees C.at atmospheric pressure for a time between about 2 and 5 minutes. 15.The method of claim 13, said first process of PECVD is applying a PlasmaEnhance CVD to the surface of said at least one layer of copper usingNH₃ and N₂ as first source gasses.
 16. The method of claim 13, saidsecond process of PECVD to the surface of said at least one layer ofcopper is exposing the surface of said at least one layer of copper to aPlasma Enhanced CVD (PECVD) treatment in a low pressure environment at achamber pressure between about. 0.3 Torr and 1.0 Torr, a temperaturebetween about 300 and 450 degrees C. exposing the surface of said atleast one layer of cooper to a second source gas.
 17. The method ofclaim 16, said second source gas being selected from the groupconsisting of N₂ and O₂ and N₂ with alkylsilane and alkylsilane.
 18. Themethod of claim 16, said second source gasses being applied at a flowrate between about 10 and 10,000 sccm, for a time of between about 3seconds and 30 minutes.
 19. A method to create a thin interface layerover the surface of a layer of copper that serves as an adhesionpromotion layer and improves adhesion between a layer of copper and anoverlying layer of ESL, comprising the steps of: providing a substrate,said substrate having been provided with at least one layer of copperover the surface thereof; pre-heating the surface of said at least onelayer of copper by applying a temperature between about 200 and 600degrees C. at atmospheric pressure for a time between about 2 and 5minutes; pre-cleaning the surface of said at least one layer of copperby applying a first process of PECVD to the surface of said at least onelayer of copper; forming an adhesive enhanced layer over the surface ofsaid at least one layer of copper by applying a second process of PECVDto the surface of said at least one layer of copper; and depositing anetch stop layer over the surface of said adhesive enhanced layer. 20.The method of claim 19, said first process of PECVD is applying a PlasmaEnhance CVD to the surface of said at least one layer of copper usingNH₃ and N₂ as first source gasses.
 21. The method of claim 19, saidsecond process of PECVD to the surface of said at least one layer ofcopper is exposing the surface of said at least one layer of copper to aPlasma Enhanced CVD (PECVD) treatment in a low pressure environment at achamber pressure between about 0.3 Torr and 1.0 Torr, a temperaturebetween about 300 and 450 degrees C. exposing the surface of said atleast one layer of cooper to a second source gas.
 22. The method ofclaim 21, said second source gas being selected from the groupconsisting of N₂ and O₂ and N₂ with alkylsilane and alkylsilane.
 23. Themethod of claim 21, said second source gasses being applied at a flowrate between about 10 and 10,000 sccm, for a time of between about 3seconds and 30 minutes.
 24. A method to create a thin interface layerover the surface of a layer of capper that serves as an adhesionpromotion layer and improves adhesion between a layer of copper and anoverlying layer of ESL, comprising the steps of: providing a substrate,said substrate having been provided with at least one layer of copperover the surface thereof; pre-heating the surface of said at least onelayer of copper by applying a temperature between about 200 and 600degrees C. at atmospheric pressure for a time between about 2 and 5minutes; pr e-cleaning the surface of said at least one layer of copperby applying a first process of PECVD to the surface of said at least onelayer of using NH₃ and N₂ as first source gasses; forming an adhesiveenhanced layer over the surface of said at least one layer of copper byapplying a second process of PECVD to the surface of said at least onelayer of copper; and depositing an etch stop layer over the surface ofsaid adhesive enhanced layer.
 25. The method of claim 24, said secondprocess of PECVD to the surface of said at least one layer of copper isexposing the surface of said at least one layer of copper to a PlasmaEnhanced CVD (PECVD) treatment in a low pressure environment at achamber pressure between about 0.3 Torr and 1.0 Torr, a temperaturebetween about 0.300 and 450 degrees C. exposing the surface of said atleast one layer of cooper to a second source gas.
 26. The method ofclaim 25, said second source gas being selected from the groupconsisting of N₂ and O₂ and N₂ with alkylsilane and alkylsilane.
 27. Themethod of claim 25, said source gasses being applied at a flow ratebetween about 10 and 10,000 sccm, for a time of between about 3 secondsand 30 minutes.
 28. A method to create a thin interface layer over thesurface of a layer of copper that serves as an adhesion promotion layerand improves adhesion between a layer of copper and an overlying layerof ESL, comprising the steps of: providing a substrate, said substratehaving been provided with at least one layer of copper over the surfacethereof; pre-heating the surface of said at least one layer of copper byapplying a temperature between about 200 and 600 degrees C. atatmospheric pressure for a time between about 2 and 5 minutes;pre-cleaning the surface of said at least one layer of copper byapplying a first process of PECVD to the surface of said at least onelayer of using NH₃ and N₂ as first source gasses; forming an adhesiveenhanced layer over the surface of said at least one layer of copper byapplying a second process of PECVD to the surface of said at least onelayer of copper using a second source gas that is selected from thegroup consisting of N₂ and O₂ and N₂ with alkylsilane and alkylsilane;and depositing an etch stop layer over the surface of said adhesiveenhanced layer.
 29. The method of claim 28, said second process of PECVDto the surface of said at least one layer of copper is exposing thesurface of said at least one layer of copper to a Plasma Enhanced CVD(PECVD) treatment in a low pressure environment at a chamber pressurebetween about 0.3 Torr and 1.0 Torr, a temperature between about 300 and450 degrees C.
 30. The method of claim 28, said second source gas beingapplied at a flow rate between about 10 and 10,000 sccm, for a time ofbetween about 3 seconds and 30 minutes.